Non-contact electromagnetic detection and sensing may be used to determine the presence or signatures (object classification or shape) of objects, or levels or the distance to the surface of materials, when other sensing methods have difficulty in providing reliable and/or accurate information. For example, in the oil and gas industry, inaccurate or unreliable tank level measurements can incur a significant loss of profitability/revenue in tank level gauging applications. An error of 1 millimeter (mm) of the level measurement in bulk storage tanks (40-80 meters in diameter) can correspond to volumetric error of several cubic meters. Since the crude oil price is generally at least $70 per barrel (1 barrel=42 US gallons; 159 liters), the 1-mm error can result in thousands of dollars loss for one or more parties involved in trading and oil transfer.
Radar has been used as a type of non-contact level gauge for the last several decades. However, radar measurements can be affected by multiple reflections inside tanks such due to tank walls, the tank bottom, the tank roof and tank obstructions including agitators, ladders and the heat coil. Furthermore, every tank generally has to use the maximum capacity for oil storage and transfer. It requires the measurements be constantly reliable as the level of product approaches the bottom or the roof of the tank.
Moreover, the electronic components and dielectric materials in conventional radar systems are temperature dependent. Radar measurement stability can be affected by temperature variations due to local weather conditions as well as a large variety of geographical locations at which the installed bases are located, such as in the Middle East (e.g., very hot) or northern poles regions (e.g., very cold). In practical applications, the limited number of tank nozzles can constrain the installation of larger sized devices, and even if there are possible additional nozzles, the costs of the large size units would be increased. Therefore, regular on-the-spot maintenance of the radar level gauges are unfortunately required due to the need of re-calibration to temperature drifts, and obstruction interferences, which incurs extra costs to customers and/or suppliers.